1. Field
The exemplary embodiments generally relate to position feedback and, more particularly, to position feedback for sealed robotic drives.
2. Brief Description of Related Developments
Generally, existing direct drive technology, which for example uses permanent magnet motors or variable reluctance motors for actuation and optical encoders for position sensing, exhibits considerable limitations when, for example, the magnets, bonded components, seals and corrosive materials of the direct drive are exposed to ultra-high vacuum and/or aggressive and corrosive environments. To limit exposure of, for example, the magnets, bonded components, electrical components, seals and corrosive materials of the direct drive a “can-seal” is generally used.
The can-seal generally isolates a motor rotor from a corresponding motor stator via a hermetically sealed non-magnetic wall or “can”, also known as an “isolation wall”. Can-seals generally use a non-magnetic vacuum isolation wall that is located between the rotor and stator of a given motor actuator. As a result, the stator can be completely located outside the sealed environment. This may allow for substantially clean and reliable motor actuation implementations in applications such as vacuum robot drives used for semiconductor applications. However, the sensors or encoders may include electronic components that may be located within the sealed environment where the electronic components may be a potential contamination source and where the sealed environment subjected the electronic components to corrosion. As may be realized, hermetically sealed connectors are required for the electronic components within the sealed environment so that wires or other signal carrying medium can be routed through the isolation wall. As may be realized, these hermetically sealed connectors may be a potential leak source. Further, in the case of optical sensors, contaminants or particulates may be deposited on the feedback track (or scale) and can lead to signal degradation and sensor failure. In other aspects, windows may be provided through which the sensors operate however these windows may also be a source of leaks.
It would be advantageous to have a position feedback system that is operative through an isolation wall between an isolated or otherwise sealed environment and an environment outside the sealed environment such that the above-described issues are addressed.